Not possible to predict the specific age of onset, severity, symptoms, and rate of disease progression from number of CAG repeats

Most individuals with HD have an affected parent

Apparent de novo cases may be explained by the death of a parent before symptom onset, unrecognized diagnosis in family, intermediate or reduced penetrance allele resulting in absent or late-onset symptoms in a parent, or non-paternity

Allele sizes may increase during paternal transmission (genetic anticipation) – results in earlier onset in the offspring of an affected male